Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$171.62	5.198%	$180.5408	$180.54	$180.55	$180.50
Purchase #2	$170.38	11.859%	$190.5854	$190.59	$190.60	$190.60
Purchase #3	$71.36	8.667%	$77.5448	$77.54	$77.55	$77.50
Purchase #4	$21.44	12.522%	$24.1247	$24.12	$24.10	$24.10
Purchase #5	$159.41	8.240%	$172.5454	$172.55	$172.55	$172.50
Purchase #6	$55.76	5.517%	$58.8363	$58.84	$58.85	$58.80
Purchase #7	$53.77	4.776%	$56.3381	$56.34	$56.35	$56.30
7 purchase totals =	$703.74		$760.5155	$760.52	$760.55	$760.30